Remove and Erase in std::deque

The std::deque (double-ended queue) container in C++ allows efficient insertions and deletions at both ends.

To remove elements from a std::deque using the remove-erase idiom, you follow a similar approach as with std::vector.

Here's an example to remove all occurrences of the number 3 from a std::deque:

1#include <algorithm>
2#include <deque>
3#include <iostream>
4
5int main() {
6  std::deque<int> Source{1, 2, 3, 4, 5, 3, 6};
7
8  // Step 1: Apply std::remove
9  auto NewEnd = std::remove(
10    Source.begin(), Source.end(), 3);
11
12  // Step 2: Erase surplus elements
13  Source.erase(NewEnd, Source.end());
14
15  // Display the result
16  std::cout << "Objects in Source: ";
17  for (auto Num : Source) {
18    std::cout << Num << ", ";
19  }
20}

1Objects in Source: 1, 2, 4, 5, 6,

In this example:

• std::remove() shifts the elements to be removed (the number 3) to the end of the std::deque.
• The erase() method then removes these surplus elements, resizing the container accordingly.

Removing Elements Based on a Condition

You can also remove elements based on a condition using std::remove_if(). Here's how you can remove all even numbers from a std::deque:

1#include <algorithm>
2#include <deque>
3#include <iostream>
4
5int main() {
6  std::deque<int> Source{1, 2, 3, 4, 5, 6};
7
8  // Step 1: Apply std::remove_if
9  auto NewEnd = std::remove_if(
10    Source.begin(), Source.end(),
11    [](int x) { return x % 2 == 0; }
12  );
13
14  // Step 2: Erase surplus elements
15  Source.erase(NewEnd, Source.end());
16
17  // Display the result
18  std::cout << "Objects in Source: ";
19  for (auto Num : Source) {
20    std::cout << Num << ", ";
21  }
22}

1Objects in Source: 1, 3, 5,

In this example:

• We use std::remove_if() with a lambda function as the predicate to remove even numbers.
• std::remove_if() moves the elements to be removed to the end of the std::deque.
• The erase() method is then used to remove the surplus elements and adjust the container's size.

Using the remove-erase idiom with std::deque ensures efficient removal of elements and proper resizing of the container. This approach can be adapted to various conditions and element types, providing a flexible solution for container management.